Endodontists use various types of instruments for cleaning and enlarging the root canals of the teeth. In a typical root canal procedure, an endodontist first makes an opening in the surface of the tooth to provide access to the interior. The endodontist then utilizes small instruments, such as hand held files and reamers, to clean and enlarge the narrow, tapered root canals. In a conventional procedure, the endodontist fills the prepared root canals with gutta percha, which is a rubber-like substance, and then seals the tooth with protective cement. The endodontists may sometimes apply a crown to the tooth as a final step.
Typically, the endodontist uses a series of delicate, flexible files to clean out and shape the root canals. Each file includes a proximal and typically including a handle to be gripped between the fingers of the endodontist and a distal end or tip. A working length with helical flutes and cutting edges is located between the proximal and distal ends. The endodontist uses files of increasingly larger diameter to sequentially increase the diameter of the root canal and achieve the desired diameter and shape.
Endodontic root canal files and reamers have been formed from twisted blanks in generally three different configurations. One type is formed by twisting a ground blank having a square cross section to create four helical cutting edges per revolution. Another type consists of a twisted blank of triangular cross section having three cutting edges per revolution. The third type, often referred to as a K-flex type, is formed from a blank having a parallelogram-shaped cross section, such as a rhomboid-shaped cross section. After twisting this type of blank, two cutting edges and two debris removal edges will be formed per revolution. All three of these types of instruments have a tapered major diameter or cross-sectional dimension and a tapered minor diameter or cross-sectional dimension in which the taper angles are generally the same. Also, the angles formed between the surfaces that define the cutting and debris removal edges are constant along the length of the instrument. In other words, a given grind angle of an edge on the instrument remains the same along the entire working length of that instrument.
Existing endodontic files and reamers formed from twisted blanks are designed in such a manner that the minor diameter is purely a function of the major diameter. The undesirable consequences of this type of design become significant for instruments that have a greater taper along the working length. In particular, these instruments become much stiffer toward the proximal end or handle of the instrument. This can cause the instrument to be difficult to maneuver within curved root canals because the instrument may not flex enough to conform to the shape of the canal. Although certain helically fluted endodontic instruments have been formed completely by grinding to achieve more constant flexibility along the length, these instruments have significant drawbacks. First, instruments formed completely by grinding are more costly to manufacture. Also, twisted instruments may be formed in a wide variety of cross-sectional shapes, depending on the shape of a initially ground wire blank.
In view of problems in this field, including those problems noted above, it would be desirable to provide an endodontic instrument, such as a file or reamer formed from a twisted blank, in which the size of one diameter or cross-sectional dimension is formed independent of the other to optimize flexibility, strength and other operating characteristics of the instrument. In this manner, instruments of greater taper may be formed with greater flexibility for maneuvering within curved root canals, while also retaining sufficient strength to resist breakage during use.